Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense:
U.S. federal	$ 3,408	$ 2,179	$ 2,107
U.S. state and local	259	272	335
Non-U.S.	386	342	416
Total current income tax expense	4,053	2,793	2,858
Deferred income tax expense (benefit):
U.S. federal	541	(45)	(23)
U.S. state and local	(7)	(8)	(5)
Non-U.S.	91	(52)	(55)
Total deferred income tax expense	625	(105)	(83)
Income tax provision (benefit)	$ 4,678	$ 2,688	$ 2,775